As semiconductor and integrated circuit technology has advanced, there has been a trend toward high-functionality integrated circuit components with numerous input and output pins, together with a demand for reduced chip size, weight, and power consumption. Consequently, as integrated circuits get smaller, they increasingly have smaller output pins arranged more closely together than ever before.
To match these integrated circuits, there is a demand for printed wiring boards to match these integrated circuits, and which therefore have small, closely arranged solder pads. However, the miniaturization of the spacing between pins is currently happening at a greater rate than the miniaturization of solder pads on printed circuit boards. Consequently, there is an interconnection technology gap for some modern devices.
To make such devices function, printed wiring boards may have extra routing layers to handle the pins of the integrated circuits, or utilize fan-out packaging. This results in the package size of an integrated circuit being larger than the integrated circuit itself, which may limit system miniaturization. In addition to these desires for miniaturized devices, it is also desirable in some cases to construct these devices from a flexible, and not brittle, substrate.
One material now being used as a substrate from which to construct thin and flexible printed wiring boards is liquid crystal polymer (LCP). The molecules in LCPs have rigid, rod-like shapes, and maintain a crystalline order when in a liquid phase or when heated and melted. The Processing and Assembly of Liquid Crystalline Polymer Printed Circuits, T. Zhang, W. Johnson, B. Farrell, and M. St. Lawrence, “The processing and assembly of liquid crystalline polymer printed circuits,” 2002 Int. Symposium on Microelectronics, 2002. discusses the construction of a printed circuit board using LCP as a substrate. A photoresist is first applied to a copper clad laminate, exposed, and developed to define a desired circuit pattern. The actual circuit is then defined by etching the exposed copper away. Holes or vias are created in the substrate via mechanical drilling. A desmearing step is then performed to remove debris from the vias or holes, thereby preparing the LCP material for metal deposition. A metalization step is next performed, and a conventional solder mask is applied to the LCP substrate. Solder is then applied through the conventional solder mask to complete the construction of the LCP printed circuit board.
While this design does allow for the creation of thin, flexible printed circuit boards, it still suffers from the same drawbacks as described above with respect to the attachment of integrated circuits with closely spaced pins thereto. As such, additional methods of connecting integrated circuits to printed circuit boards are needed.